1. Field of the Invention
The present invention relates to an abnormality detecting device having a function for detecting an abnormality in a spindle or a spindle motor of a machine tool, and relates to an abnormality detecting method.
2. Description of the Related Art
In many cases, malfunction of a spindle of a machine tool or a spindle motor for driving the spindle is due to deterioration or breakage of a bearing of the spindle or the spindle motor. If the machine tool is operated when the spindle has a complete malfunction, processing accuracy of a workpiece is deteriorated and the workpiece will become a defective product. In addition, when it takes a time to restore the spindle, the machine tool must be suspended for a long time, whereby an operation rate of the machine tool is lowered.
Therefore, by detecting a symptom of a failure (or deterioration) of the spindle before the spindle has a complete malfunction and taking appropriate measures (for example, repairing the spindle), the suspension time (or downtime) can be reduced and the operation rate of the machine tool can be improved. In the prior art, a method for measuring deterioration of vibration of a spindle or a spindle motor, and a method for detecting an abnormal noise thereof are known as a method for detecting an abnormality of the spindle.
For example, JP 2005-074545 A discloses a status monitoring device for a machine tool, and it is described that vibration data is measured by using an AE sensor, an amplifier and a bandpass filter after receiving a spindle rotation command and a feed axis drive command, and then, the number of times, that the vibration data exceeds a threshold calculated from spindle rotation information, is counted by a level counter. Then, the counted number is compared to an alarm level so as to judge the status of the spindle, and an alarm is displayed on an alarm display if necessary.
Further, JP 2001-259972 A discloses a magnetic bearing unit for a machine tool, and it is described that, by providing: a vibration detecting means for detecting vibration of a spindle; a frequency characteristic variable filter for extracting a vibration component synchronized with the rotation of the spindle from an output signal of the vibration detecting means; and a judging means for judging a state in which a level of the output signal extracted by the variable filter exceeds a specified level as an abnormal state, the abnormal state such as mounting failure or rotational fault of a tooling can be automatically detected, whereby processing deficiency of a workpiece can be reduced.
In order to detect vibration of a spindle, it is necessary to attach vibration measuring equipment, etc., to the spindle or a spindle motor. When the vibration is manually detected, an operator must hold the measuring equipment in his/her hand and measure the vibration of each component of the machine tool at regular intervals, which is a big burden on the operator. On the other hand, the vibration of the spindle can be automatically detected by a vibration sensor, etc. In this case, however, the vibration sensor must be always attached to the spindle, whereby cost of the machine tool is increased.
When an abnormality of a spindle is detected by catching an abnormal noise of the spindle, the abnormality of each component of the machine tool is periodically and aurally rally detected by the operator, which is also a big burden on the operator. On the other hand, the abnormal noise can be automatically detected by a microphone, etc. In this case, however, it is difficult to appropriately detect the abnormal noise since a factory in which the machine tool is installed is very noisy, and further, it is costly to arrange the microphone.